Williams' best finish at this event was runner-up five years ago, the same year Sharapova made the field as a 15-year-old qualifier and lost in the first round.

Williams struggled in the first set, which featured several long games. She won one game after it went to deuce seven times. But in the third set, Sharapova won just four points in the first five games.

"I gave it all I had in the first two and I think I ran a little bit short," the world's fourth-ranked player said. "My body is adjusting to the clay faster. I'm moving on it a lot better than I used to."

Cornet, an 18-year-old in her second season on the tour, also reached the semifinals at Amelia Island last week. Ranked No. 40, she has never faced Williams but watched her play Friday.

"I said 'Oh my God, if I play Serena tomorrow, I hope not to be ridiculous,'" she said. "I think I will do what I do usually. I will use my topspin forehand. I will run everywhere I can and I will just do my best and fight on every point."